Bioclimatic stress, heat perception and asthma attacks in young adults in Natitingou (Benin, West Africa)

Climate variability and the intensification of bioclimatic discomfort are major environmental factors influencing respiratory health in tropical cities. In Natitingou, a municipality in northwestern Benin characterized by a marked alternation between dry and rainy seasons, the population is regularly exposed to challenging bioclimatic conditions, exacerbated by the harmattan wind, high temperatures, and humidity fluctuations. This study analyzes the influence of bioclimatic discomfort on the frequency of asthma attacks in young adults aged 18 to 35 years. The methodological approach relies on the use of climatological data covering the period 1993–2024, obtained from the National Meteorological Directorate of Benin and NOAA, combined with perception data collected through surveys. Bioclimatic conditions were characterized using the UTCI (Universal Thermal Climate Index), calculated from air temperature, relative humidity, wind speed, and radiation, at monthly and three-hourly timescales. Perceived discomfort and the frequency of asthma attacks were assessed using self-reported data on a five-level ordinal scale. The results highlight a marked seasonality in UTCI, with average monthly values ranging from 26.2°C in January and December to a maximum of 34.5°C in April. The March–May period sees the highest levels of heat stress, with values exceeding 32°C, corresponding to the high heat stress class, while a second peak is observed in October at 32.2°C. On a three-hour scale, UTCI varies from 23.9°C at 6:00 a.m. to a maximum of 34.4°C at 2:00 p.m., identifying the 12:00 p.m.–4:00 p.m. period as the period of maximum stress. These high levels coincide with a significant deterioration in bioclimatic perception, with the proportion of negative perceptions reaching 62% in April and up to 65% at 2:00 p.m. This correlation suggests a potential increase in the frequency of asthma attacks during the most stressful periods and time slots. This study highlights the importance of integrating bioclimatic environments into asthma prevention strategies in tropical urban settings, in order to anticipate periods of risk and guide public health actions.